1. Field of the Invention
The present invention relates to gears and a gearing apparatus for transmitting a rotational motion between two associated shafts, i.e., from one to the other of two associated shafts, through a pair of gears which are engaged with each other so that teeth of the engaged gears are operatively mated with each other. More particularly, the present invention relates to gears and a gearing apparatus capable of reducing generation of noise during the rotational motion transmitting operation of a pair of gears engaged with each other, and also reducing an error in transmission of the rotational motion.
2. Description of the Related Art
As gears in a conventional gearing apparatus, typically, gears called standard gears having symmetrical tooth profiles are used. In a combination of such standard gears, the tooth tip and the tooth root of each of teeth have identical tooth widths when measured in a direction along the axes of the respective gears and the total tooth depth of each tooth is unchanged and constant in a tooth width direction. Therefore, in the case where opposite teeth are mated with each other, since an amount of change in a spring constant of a tooth which functions as a type of spring between the double-teeth-mating arrangement and the single-tooth-mating arrangement, is large, sometimes, noise due to the mating of the gear teeth becomes large and also the vibration is increased. Further, the increase in the vibration of the mated gear teeth could often cause an increase in an error in the rotation transmission of the engaged gears.
In order to cope with the above problems, there has been conventionally proposed a gearing apparatus in which a pair of gears is configured by involute spur gears and at least one gear of the pair of gears is provided with rigidity reducing means incorporated therein for reducing the rigidity in the double-teeth-mating region of the said one gear, in comparison with the rigidity to be provided by the standard involute spur gear. As this rigidity reducing means in the gear, for example, there is a through-hole formed in a gear, which runs through from one of end face of a tooth tip portion toward the other end face thereof. In this case, when opposite teeth are mated with each other, a deflection amount of the tooth is relatively increased, in comparison with a deflection amount of a tooth of the standard involute spur gear, and therefore, the fluctuation in the deflection amount in the duration of mating of the opposite teeth is suppressed and accordingly, the silence during the rotation transmission time is improved, and also, the vibration is reduced (refer to Japanese Unexamined Patent Publication No. 8-312755 (FIG. 4)).
However, in the gears of the conventional gearing apparatus, as shown in FIG. 4 of Japanese Unexamined Patent Publication No. 8-312755, although the through-hole as the rigidity reducing means runs through from the one end face of the tooth tip portion to the other end face thereof, a tooth profile of each tooth is still kept as an involute spur tooth profile, and the tooth contact at the time of mating of each tooth with each tooth of the mating gear is in a line contact state. In this case, in the mating of the opposite teeth, the line contact state is maintained from the beginning to the end in the mating, and therefore, it is impossible to appreciably reduce noise generated when the pair of gears is mated with each other. Also, it is impossible to sufficiently improve the vibration suppression at the mating time, and also, to sufficiently reduce the error in the rotation transmission of the gearing apparatus.